One of the important components of a gas turbine is the so-called combustion chamber in which fuel is burnt with the aid of an oxidizer. The oxidizer typically involves air. The hot gas produced during combustion in the combustion chamber is conveyed onwards to a turbine.
What is referred to as the burner is located on the side of combustion chamber facing away from the turbine. This is used for igniting the fuel or the fuel-air mixture and is equipped with ignition electrodes for this purpose. The fuel and the air are injected through openings of the burner into the combustion chamber. The ignition electrodes are arranged in the vicinity of these openings and ignite the gas flowing past there. To this end an ignition spark is generated by applying an ignition voltage between two ignition electrodes. This ignition spark is present during the entire ignition duration. To obtain an optimum ignition spark a specific gap must be maintained precisely between the tips of the ignition electrodes.
Previously the ignition electrodes were frequently fixed to the outside surface of the burner with the aid of a clamp. In such cases the ignition electrodes are clamped rigidly in the clamp with the aid of a screw arranged centrally between the ignition electrodes. Typically the support surfaces of the ignition electrodes rest on their full circumference on their clamp which can for example have a round cross section. In the area of the clamp the ignition electrodes are usually surround by a ceramic shroud. The ceramic shroud is used for electrical insulation of the ignition electrodes and thus reduces the heat-related expansion. Fluctuations in the surface quality of the ceramic and inaccuracies in the form and the position of the clamp can lead to the ignition electrodes not being able to be fixed correctly. The fixing is either too firm or too loose. In the event of the fixing being too film the thermal expansion of the ignition electrodes is prevented and in the event of the fixing being too loose undesired vibrations of the ignition electrodes occur.
Typically the ignition electrodes are not arranged centrally between a so-called diagonal mesh and a burner carrier, since the clamps used for fixing the ignition electrodes are frequently screwed to a cam which has a certain height because of the minimum screw depth. The distance from the diagonal mesh is thus small and the result can be a sparkover in this area if the gap at this point is smaller than at the so-called spark gap at which the ignition sparks are to be generated. The result of this is that the burner involved can no longer be ignited directly.
A further difficulty of the ignition electrode fixings used previously lies in their sensitivity to impacts during installation and dismantling and also during transport of the burner. The ignition electrode glued into a ceramic normally does not rest directly on the burner. This can thus quickly result in bending and breakage of the ignition electrodes which makes it necessary to replace the ignition electrodes.